[iOS] React Native's headers fail a Swift import built with SWIFT_TREAT_WARNINGS_AS_ERRORS (nullability and deprecation warnings)

Read PR #59240 to see the prior fix pattern for nullability warnings. Edit RCTWebSocketModule.h:23, RCTReactTaggedView.h:29, RCTRedBox+Internal.h, RCTRedBox2Controller+Internal.h, RCTRedBox2ErrorParser+Internal.h and RCTUIConfiguratorProtocol.h:40 to add missing nullability specifiers or drop deprecated RCTRootView. Build the linked reproducer with SWIFT_TREAT_WARNINGS_AS_ERRORS=YES; done when xcodebuild emits no pcm errors.

Description

An app or a library whose Swift target sets SWIFT_TREAT_WARNINGS_AS_ERRORS = YES cannot import React Native's modules: Xcode precompiles the imported Clang module with the target's warnings as errors, and React Native's own public headers warn there. This happens on main, with both the default prebuilt core and a source build.

https://github.com/react/react-native/pull/59240 fixed the same kind of warning in RCTHTTPRequestHandler.h and RCTMultipartDataTask.h. These headers still warn on main (f1f1474058; the nightly I ran is e57dcb3cc, four commits behind, and its copies of these headers match main):

• React/CoreModules/RCTWebSocketModule.h:23: typedef SRWebSocket * (^SRWebSocketProvider)(NSURLRequest *request); is inside NS_ASSUME_NONNULL, but the block typedef's pointers are not inferred, so -Wnullability-completeness fires.
• React/Fabric/Utils/RCTReactTaggedView.h:29: - (BOOL)isEqual:(id)other; inside NS_ASSUME_NONNULL makes the parameter nonnull, which conflicts with NSObject's nullable id.
• React/CoreModules/RCTRedBox+Internal.h, RCTRedBox2Controller+Internal.h and RCTRedBox2ErrorParser+Internal.h: each has nullable members and no NS_ASSUME_NONNULL region, so every other pointer warns.
• Libraries/AppDelegate/RCTUIConfiguratorProtocol.h:40: - (void)customizeRootView:(RCTRootView *)rootView; uses the deprecated RCTRootView, so -Wdeprecated-declarations fires in the module build.

The source build stops at the first module that fails (React_RCTAppDelegate), so it does not reach RCTWebSocketModule.h, which the prebuilt run shows.

Steps to reproduce

The reproducer is the reproducer template with [email protected] (built from main), @react-native-community/[email protected] (the nightly needs it for autolinking), and SWIFT_TREAT_WARNINGS_AS_ERRORS = YES on the app target. The template's SceneDelegate.swift already has import React and import React_RCTAppDelegate. No simulator or signing is needed.

1. cd ReproducerApp && npm install
2. cd ios && pod install
3. xcodebuild -workspace ReproducerApp.xcworkspace -scheme ReproducerApp -configuration Debug -sdk iphonesimulator -destination 'generic/platform=iOS Simulator' CODE_SIGNING_ALLOWED=NO build
4. Then RCT_USE_PREBUILT_RNCORE=0 pod install and the same xcodebuild command, to build React Native from source.

Expected: the app builds, since nothing in it warns.

Seen: ** BUILD FAILED ** in SwiftExplicitDependencyGeneratePcm, on warnings in React Native's headers (see the logs below).

React Native Version

0.89.0-nightly-20261031-e57dcb3cc

Affected Platforms

Runtime - iOS, Build - MacOS

Output of npx @react-native-community/cli info

System:
  OS: macOS 27.0.1
  CPU: (8) arm64 Apple M1
  Memory: 500.36 MB / 8.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 26.12.1
    path: /Users/yevhenii/.nvm/versions/node/v26.12.1/bin/node
  Yarn: Not Found
  npm:
    version: 12.2.1
    path: /Users/yevhenii/.nvm/versions/node/v26.12.1/bin/npm
  Watchman:
    version: 2026.10.19.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.17.0
    path: /opt/homebrew/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 27.2
      - iOS 27.2
      - macOS 27.2
      - tvOS 27.2
      - visionOS 27.2
      - watchOS 27.2
  Android SDK: Not Found
IDEs:
  Android Studio: Not Found
  Xcode:
    version: 27.2/27B52
    path: /usr/bin/xcodebuild
Languages:
  Java: Not Found
  Ruby:
    version: 4.0.9
    path: /opt/homebrew/bin/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 21.0.0-alpha.1
    wanted: 21.0.0-alpha.1
  react:
    installed: 19.3.0
    wanted: 19.3.0
  react-native:
    installed: 0.89.0-nightly-20261031-e57dcb3cc
    wanted: 0.89.0-nightly-20261031-e57dcb3cc
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: Not found
  newArchEnabled: false

Stacktrace or Logs

# step 3, default prebuilt core (paths below the temporary folder shortened to …/)
…/derived-data/Build/Products/Debug-iphonesimulator/XCFrameworkIntermediates/React-Core-prebuilt/React.framework/Headers/RCTReactTaggedView.h:29:21: error: conflicting nullability specifier on parameter types, 'nonnull' conflicts with existing specifier 'nullable'
…/derived-data/Build/Products/Debug-iphonesimulator/XCFrameworkIntermediates/React-Core-prebuilt/React.framework/Headers/RCTWebSocketModule.h:23:21: error: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified)
<unknown>:0: error: failed to emit precompiled module '…/derived-data/Build/Intermediates.noindex/SwiftExplicitPrecompiledModules/React-EB9M1Z4OHNICYJK47EJBN2CQ0.pcm' for module map '…/derived-data/Build/Products/Debug-iphonesimulator/XCFrameworkIntermediates/React-Core-prebuilt/React.framework/Modules/module.modulemap'
** BUILD FAILED **

The following build commands failed:
	SwiftExplicitDependencyGeneratePcm arm64 …/derived-data/Build/Intermediates.noindex/SwiftExplicitPrecompiledModules/React-EB9M1Z4OHNICYJK47EJBN2CQ0.pcm

# step 4, RCT_USE_PREBUILT_RNCORE=0
…/ReproducerApp/ios/Pods/Headers/Public/React-Core/React/RCTRedBox+Internal.h:17:44: error: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified)
…/ReproducerApp/ios/Pods/Headers/Public/React-Core/React/RCTRedBox2Controller+Internal.h:20:4: error: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified)
…/ReproducerApp/ios/Pods/Headers/Public/React-Core/React/RCTRedBox2ErrorParser+Internal.h:17:38: error: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified)
…/ReproducerApp/ios/Pods/Headers/Public/React-Core/React/RCTRedBox2ErrorParser+Internal.h:41:24: error: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified)
…/ReproducerApp/ios/Pods/Headers/Public/React-Core/React/RCTRedBox2ErrorParser+Internal.h:41:54: error: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified)
…/ReproducerApp/ios/Pods/Headers/Public/React-RCTAppDelegate/RCTUIConfiguratorProtocol.h:40:28: error: 'RCTRootView' is deprecated: This API will be removed along with the legacy architecture.
<unknown>:0: error: failed to emit precompiled module '…/derived-data/Build/Intermediates.noindex/SwiftExplicitPrecompiledModules/React_RCTAppDelegate-B8C35ZXJIXKD5SNK3CAGCPF8S.pcm' for module map '…/ReproducerApp/ios/Pods/Headers/Public/React_RCTAppDelegate/React-RCTAppDelegate.modulemap'
** BUILD FAILED **

The following build commands failed:
	SwiftExplicitDependencyGeneratePcm x86_64 …/derived-data/Build/Intermediates.noindex/SwiftExplicitPrecompiledModules/React_RCTAppDelegate-B8C35ZXJIXKD5SNK3CAGCPF8S.pcm

macOS 27.0.1, Xcode 27.2 (27B52), Apple Swift 6.4.2, CocoaPods 1.17.0, Node 26.12.1, npm 12.2.1.

https://github.com/react/react-native/issues/57524 reported the RCTWebSocketModule.h warning under the prebuilt path in 0.86.0 and was closed without a reproducer.

MANDATORY Reproducer

https://github.com/YevheniiKotyrlo/react-native-react-core-headers-warnings-as-errors

Screenshots and Videos

No response